1. Technical Field
The invention relates to an apparatus and to a method for determining the dynamic camber of vehicle tires. More particularly, the invention relates to such an apparatus and method which measure the dynamic camber on a vehicle tire in an actual operating road environment, wherein changes in road surface and inclination affect the camber. Even more particularly, the invention relates to such an apparatus and method in which the camber angles measured throughout a particular road surface are stored in a computer and reused at a test facility for testing other tires in a controlled environment while impressing on the subsequent test tires actual cambers which the tires would experience under actual road operating conditions and when used with a particular vehicle.
2. Background Information
Various complicated, bulky and expensive equipment has been developed for statically measuring camber on a tire, which is one of the factors tested to determine tire wear and ride characteristics. These prior art systems and equipment are expensive and difficult to operate for performing repeated tests on numerous tires in order to gather sufficient data for determining the effects of camber on a particular tire.
The measurement of camber on a tire and its effect on the wear and ride characteristics thereof, is only one of a number of tests performed on tires to ensure that the tire performs satisfactorily, and in particular, that the tire performs satisfactorily on specific vehicles.
The trend in the tire and automobile industry today is to closely match and design a particular tire as original equipment for a particular vehicle. Thus, automobile manufacturers, in selling the vehicle, will have mounted thereon a particular tire which has been found to provide the most desirable wear and ride characteristics for that particular vehicle and tire.
In order to ensure that the tire provided for a particular vehicle provides the desired results, various tests are performed on prototypes of such tires on the actual vehicle. However, it is difficult for a tire manufacturer to obtain the actual vehicle intended for future production for a sufficient length of time in order to perform all of the tests desired and then repeat the tests on various tires and modifications thereto, in order to arrive at the optimum tire design. The automobile manufacturers usually permit the tire manufacturers to use one of its prototype vehicles for a relatively short period of time and at a facility remote from the tire manufacturer's laboratory to test its prototype tire intended for use on that vehicle when it becomes a future production model.
Heretofore, the effect of camber on a vehicle tire was obtained in a laboratory tire test facility, wherein a road or load wheel is engaged with a test tire and the angle of inclination or camber of the test tire with the road wheel is varied during test cycles. However, such a test does not provide for a real-world environment, nor account for the effect that the structure of a particular vehicle, such as its suspension system, weight and driving characteristics, have on the camber angle which is impressed upon the tire, which then affects the wear characteristics of the tire.
Various prior art devices, some of which use lasers, have been utilized for alignment and for statically measuring both camber and caster in wheel mechanisms, as shown in the following patents.
U.S. Pat. No. 4,898,464 discloses a method and apparatus for determining the position of an object so that the steerable wheels of the vehicle may be aligned. The mechanism includes a microcomputer, a laser, mirror and phototransistor laser ray. The laser light is both emitted and received to provide the information needed to align the steerable wheels of the vehicle.
U.S. Pat. No. 2,077,082 discloses a device that measures both the camber and caster in wheel mechanisms. The measuring device is installed on a shaft of a spindle to allow the camber and caster readings to be taken with the vehicle resting on the floor. The weight distribution for the vehicle will go up upon all the wheels, attempting to simulate actual road conditions.
U.S. Pat. No. 3,963,352 discloses a wheel alignment apparatus wherein a sensor unit is provided which includes a casing, mirror and magnet. The sensor unit is secured to the axle housing of the wheel by use of the magnet. The sensing unit includes a light source and light-sensitive devices. The light is directed to and reflected back from the mirror to provide the measurement necessary to determine the caster and camber of the wheels.
U.S. Pat. No. 4,578,870 discloses a selectable beam/plane-projecting laser and alignment system for a vehicle body and frame. A laser is attached to the vehicle through a carrier bar, and a switching mechanism has a holder member and slide member that is utilized to alternate between a beam of light or plane of light. The plane of light may be projected in any direction orthogonal to the mounting bars.
U.S. Pat. No. 4,454,659 discloses an adjustable carriage assembly utilized in a body alignment device. The adjustable carriage assembly is provided with a measurement bar which is secured to the vehicle, and has a laser sighting instrument attached thereto.
Although certain of these prior art alignment systems use lasers to enable the camber of the vehicle tires to be determined, none of these prior art patents, nor other known prior art devices, provide a device which is attached to a moving vehicle in order to obtain the dynamic angles of camber which the tire experiences as it moves along an actual road surface on a particular moving vehicle.
Therefore, the need exists for an improved apparatus and method for determination of the dynamic camber on a vehicle tire, performed while the tire is moving along an actual road surface and mounted on an actual vehicle of the type on which the tire will be used, which data can then be used at a tire test facility on other test tires in order to test various modifications and changes to a tire in order to arrive at the optimum tire design for a particular vehicle.